The present invention relates to a sheet feeding apparatus for an electrostatic copying machine or the like.
In an electrostatic copying machine, the feeding of sheet copy paper is an important functional requirement among many, each of which is essential to provide a duplicate copy, or copies of an original document.
The means for accomplishing separation and feeding of a single copy sheet is relatively well known within the copier field. Usually, a pair of round wheels, fabricated from highly frictionable material are rotatably driven for the purpose of separating and advancing single sheets of copy paper seriatim from the supply stack held within a tray or cassette.
Once separated from the stack, the single sheet is further advanced by the separator feed wheels to a registration gating device for alignment and timing purposes.
From the registration gate area, the sheet is transported further through the use of additional transport rollers or belts which are arranged in the path of travel for that purpose. Each sheet is finally directed towards the process portion of the copier where transfer of the developed image occurs. In order to achieve precise duplication, the timely arrival of the leading end of each copy sheet must precisely register with the leading edge of the developed image being carried upon the photoconductor. If there is any mismatch in the relationship of the developed image to the copy sheet, an undesirable effect is immediately seen by the machine operator, not having received the desired duplicate copy of the original document.
In order to achieve registration of the copy sheet to the developed image, various arrangements of gating mechanisms or synchronous sheet feeding rollers are used. These devices are used in combination with a slight resilient buckle induced into the leading portion of the sheet in order to ensure registration. Once the leading end of the copy sheet does communicate with the developed image, the transfer portion of the copier process proceeds until all of the image is transferred to the sheet.
While the registration gate is provided in several different forms, one of the most common involves the use of sheet feeding rollers. These rollers are usually kept stationary during a part of the initial feeding stage of the copy sheet. Then, at a predetermined time, when the sheet is registered the stopped sheet feeding rollers are rotatably engaged through a clutching device.
Another form of registration gate comprised of mechanical fingers is used where the fingers are raised from the path of the stopped sheet at a predetermined time when a mechanically connected actuator is energized. Usually, the sheet feeding rollers used with this system do not stop, and a certain amount of slippage upon sheets is permitted to allow the rollers to continue running, thereby eliminating errors in registration due only to inertial considerations.
In any case, the sheet registration gate provides a means to straighten out any skew inherent in the copy sheet, prior to advancement to the transfer function in the process. Also, the resilient buckle provided in the leading edge of each temporarily stopped sheet, provides an opportunity for the sheet's leading edge to assume a parallel alignment with respect to the gate. The imposed buckle also insures that the sheet's lead edge is positioned at the roller nip for further positive advancement to the process area.
Since the transferred image is not permanent, a further transport system engages the copy sheet on the non-image side, thereby conveying the sheets seriatim to the fixing stage of the copying process.
The drive apparatus for advancing the sheets typically includes rotatable members actuated by electromagnetic clutching devices, which are usually driven from an endless drive member such as a chain which transmits power for other components within the copier. There are also similar rotational control clutching devices in the form of wrap spring clutches which are actuatable by separate electrically powered delatching devices. These electrical clutching devices require a means of energization from a main power source, as well as logic and circuitry, all of which contribute to the complexity and cost of manufacturing, assembly and servicing of a copier machine.
While the clutching devices previously described are practically used as standard equipment in copiers, and used to accomplish all of the separation, feeding and advancement of copy sheets, as well as other functions, these devices are expensive and space consuming. It is also fairly complex to provide means for timing the clutches so that registration is endlessly repeatable in a stream feeding situation where multicopy is required by a machine operator. There are adjustments provided within the electromagnetic clutch systems which correct for error, or an adjustment may be accomplished through a paper sensing switch located to feed the position of the sheets in their respective paths of travel. The paper sensing switch adjustments are especially difficult to achieve, and require complicated assembly procedures as well as access and procedures for service requirements.